Protection of Prior SARS-CoV-2 Infection Against Different Variants, Including Omicron Descendants, in a Country with High Viral Transmission.

Background: Prior infection with SARS-CoV-2 has been reported to confer protection against reinfections. Because Peru has been affected by several variants of this virus, it is an ideal location to better explore this phenomenon. In this study, we aim to evaluate protection of prior SARS-CoV-2 infection against reinfection by variants during the COVID-19 pandemic in Peru.

Methods: A nested case-control study was carried out, using national data from Peru between 2021 and 2023. Five study periods were defined, delimited by the predominance of the main SARS-CoV-2 variants circulating during the pandemic. Cases were paired with controls in a 1 to 4 rate by sex, age, region, being a health worker, and the week of infection. Protection was calculated using conditional logistic regression to estimate odds ratios (OR) with 95% confidence intervals (95% CI) expressed as (1-OR) x100.

Results: Protection from prior infection against SARS-CoV-2 reinfection was 86.3% (95% CI, 81.8 to 89.7) for Lambda, 73.0% (95% CI, 62.9 to 80.3) for Gamma, 84.7% (95% CI, 82.1 to 86.9) for Delta, 34.9% (95% CI, 25.5 to 43.1) for Omicron BA.1, 67.0% (95% CI, 58.7 to 73.6) for Omicron BA.2.12.1, 49.1% (95% CI, 40.5 to 56.5) for Omicron BA.4, 44.8% (95% CI, 39.9 to 49.3) for Omicron BA.5, 29.4% (95% CI, 18.2 to 39.1) for Omicron BQ, and 8.6% (95% CI, -0.5 to 16.9) for Omicron XBB.

Conclusions: Prior infection provides significant protection against SARS-CoV-2 reinfection episodes, although this varies widely among the different Omicron sublineages.